<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Bootstrap Learning</title>

    <!-- 最新版本的 Bootstrap 核心 CSS 文件 -->
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">

    <!-- 可选的 Bootstrap 主题文件（一般不用引入） -->
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/css/bootstrap-theme.min.css" integrity="sha384-rHyoN1iRsVXV4nD0JutlnGaslCJuC7uwjduW9SVrLvRYooPp2bWYgmgJQIXwl/Sp" crossorigin="anonymous">

    <!-- 最新的 Bootstrap 核心 JavaScript 文件 -->
    <script src="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>

    <link rel="stylesheet" href="index.css">
</head>
<body>
    <div id="app">
        <div class="container">
            <div class="row">
                <div class="col-sm-5 col-xs-12">
                    1
                </div>
                <div class="col-sm-2 col-xs-6">
                    <div class="upper">
                        upper part
                    </div>
                    <div class="under">
                        under part
                    </div>
                </div>
                <div class="col-sm-2 col-xs-6">3</div>
                <div class="col-sm-3 col-xs-12">4</div>
            </div>
        </div>
    </div>
</body>
</html>